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The final exam

The final exam. Mon, 8p WGND 115 Comprehensive “Essentials of CSS 305” on BB Don’t forget calculator! Review Exams 1 and 2 and labs and homework assignments (especially practice problems). Erosion:. A process that transforms soil into sediment

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The final exam

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  1. The final exam • Mon, 8p WGND 115 • Comprehensive • “Essentials of CSS 305” on BB • Don’t forget calculator! • Review Exams 1 and 2 and labs and homework assignments (especially practice problems)

  2. Erosion: • A process that transforms soil into sediment • Natural = geologic erosion: weathering means soil formation usually > soil loss • Human-induced • over-grazing – 1/3 of all land degradation, • forest harvest – in rain forests, bad practices responsible for 0.5 b ha of land degradation…so far • Tied with damage to plant communities (increasing susceptibility to erosion) • 85% of degradation of soils is due to the destructive action of wind & water (2/3 of that is by the action of water) Estimated cost in US $9-$44 billion annually!!!

  3. Geologic erosion - greatest in semi-arid environments

  4. Soil degradation • Physical properties: compaction, crusting • Chemical properties: acidification, salt accumulation • Erosion (loss): wind & water

  5. Downward spiral of land degradation Degraded land gpoor cropsghuman povertyg reduced protection of soil resources gincreased erosiongdesperate people clear, cultivate, & degrade more land

  6. Easter Island - Volcanic PM, equatorial climate… 1st settlers – 400ad – rich in plant and animal resources Building of moai (statues) by 1400 – the two native trees (one palm one woody) were extinct Rapid and catastrophic loss of forest nutrients and soil erosion Consumed the birds & fisheries till they ran out Ate rats to survive – cannibalism emerges – societal breakdown Abandon villages – moved to caves The most total environmental and social breakdown in recorded history

  7. Factors affecting rates of erosion Factoid: Approximately 53% of all wood consumed globally is used for home heating and cooking.(Bowyer et. al., Forest Products and Wood Science: An Introduction. Iowa State Press 2003. p.ix) • Topography • Land use practices • Vegetation type • Rainfall amount, frequency, and intensity • Soil chemical properties (high CEC = more plant cover = less erosion)

  8. Effect of agriculture Fig 17.5, Brady & Weil health hazard too!

  9. Erosion mechanics Factoid: large raindrops fall at 30 km/hr ! • Detachment • Transport • Deposition Most erosion is initiated by the impact of raindrops, NOT by the flow of running water Fig. 13.8, p. 333

  10. USLE - Universal Soil Loss Equation A = RKLSCP • R= rainfall erosivity • K= soil erodibility • L = slope length • S = slope steepness • C = cover and management • P = erosion-control practices Soil-related factors Land management factors In 1990s Revised (RUSLE) computer-based, more data, improved more sophisticated modeling See Table 17.3 of Brady & Weil for details

  11. (cm/hr) K: soil erodibility factor A = RKLSCP • Infiltration capacity • Structural stability (next slide)

  12. K: soil erodibility factor A = RKLSCP • Infiltration capacity (previous slide) • Structural stability • Particle cohesion • frictional resistance (block vs. sphere) • cementation by OM, clays • Particle mass (2.0 g/cm3 for bauxite, 5.3 for hematite, 7.6 for galena)

  13. Soil properties resulting in low K values (less erosion) • High organic matter content • Non-expansive clays • Strong granular structure • “stoniness” & macropores

  14. Practices that minimize erosion A = RKLSCP L = slope length S = slope steepness C = cover and management • Mulching - C • Contour cultivation – C, L & S • Grass contour hedges - L

  15. 1. Mulch as a means to reduce erosion A = RKLSCP C =cover and management

  16. Effects of mulching, contour cultivation, and grass hedges

  17. A few practices to reduce soil loss caused by timber production • Tree removal: cable not skidder • Scheduling: when dry or frozen. snow great. • Road design: 99% of soil loss avoided by gravel, planting grasses on road cuts • Buffer strips: 1.5 times the height of the tallest trees

  18. Wind erosion mechanics • Detachment • Transport • Deposition Wind erosion Surface creep, saltation, suspension. • 40% of eroded soil is transported by wind erosion in USA • In six of the Great Plains states, wind erosion exceeds water erosion • Fine particles (aeolian dust)can even be transported to other continents (Saharan sands found in Hawaii)

  19. Dust Bowl – 1930’s United States, great plains

  20. Factors affecting wind erosion • Wind velocity > 25 km/h to get started – After which soil movement is proportional to the cube of the wind velocity • Wind turbulence– though it’s the airborne particles that do most of the abrasion/erosion • Surface roughness - decreases wind erosion • Vegetation - decreases wind erosion • Soil properties – Aggregate & surface crust stability, bulk density E = ICKLV I – soil erodibility C – climate K - soil roughness L – field width V – veg cover Naturally, there is a wind erosion prediction equation . . .

  21. Controls of wind erosion • Add moisture: often not practical • Conservation tillage • stubble mulch • strip-cropping perpendicular to the wind • if tilling, do so when soils moist, not dry • Windbreaks: trees best, but even cereal crops can help!

  22. Coming full circle . . .

  23. Soil is: A natural, evolutionary body that is the product of the environment under which it develops…

  24. The real voyage of discovery consists not in seeking new landscapes but in having new eyes. ~ Marcel Proust

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